The present disclosure relates generally to power control topologies in electrical circuits.
Power control topologies are typically designed to regulate an output voltage or current to an electrical system. Power control topologies monitor a feedback output voltage or current from a closed loop system and regulate the power provided to the closed loop system based on the feedback output voltage and/or current. While there are many different control topologies available to close the feedback loop, they may be generally grouped into two types: pulse-width modulation (PWM) or hysteretic.
One conventional PWM power control topology is voltage-mode control. Voltage-mode topologies use an error amplifier to compare feedback output voltage to an internal reference voltage. Voltage-mode topologies have a fairly simple design, are fairly noise immune, and also can employ a clock to control a switching frequency of the circuit which can allow the circuit to be synchronized to an external clock source. However, the main disadvantage of voltage-mode topologies is that the voltage mode control introduces a double pole in the power stage, which can typically have a low frequency. This low frequency limits the loop bandwidth and thus the transient response in the power supply.
Hysteretic control is an extremely simple control topology. A comparator with some small hysteresis between its terminals compares the feedback output voltage of the closed loop system directly to a high-accuracy reference voltage and controls the power gate driver accordingly. The advantage of such a direct control over the output voltage is the speed and transient response of the control loop. When the output voltage changes due to a transient, the reaction time of the control loop to the transient is limited only by the propagation delays in the comparator and power gate driver. There is no low-bandwidth error amplifier for an error signal to travel through.
Thus, the hysteretic topology is a very fast and efficient control topology. Additionally, its simplicity of operation inherently stabilizes the closed loop system without any required loop compensation. This simplicity also helps reduce the cost of the control topology. Hysteretic control topologies typically do not include an oscillator or error amplifier to design, build, and test. A basic hysteretic comparator simply controls the switching action of the power supply. The primary disadvantage of hysteretic control topologies in its fundamental form is the switching frequency variation associated with the hysteretic control topology. The switching frequency of a hysteretic control topology is not set by a clock or synchronization signal. Instead, the switching frequency is set by the hysteresis amount in the control system, as well as the external components and operating conditions of the electrical system. Large frequency variations associated with hysteretic control topologies can make them unsuitable for certain applications such as medical or industrial automation systems which require more controlled or consistent switching frequencies.
What is needed then are improvements in power control topologies.